Sorting Three Groups
A medium-tier problem at 42% community acceptance, tagged with Array, Binary Search, Dynamic Programming. Reported in interviews at UiPath and 0 others.
Sorting Three Groups is a medium-difficulty array problem that appears in UiPath assessments. You're given an unsorted array and need to segregate elements into three groups in linear time without relying on a full sort. The 41% acceptance rate hints at a trick most candidates miss on first read: the optimal solution trades the intuitive sort() call for a two-pointer or counting approach that processes the array in a single pass. If you hit this on a live OA and blank on the pattern, StealthCoder surfaces a working solution invisible to the proctor in seconds.
Companies that ask "Sorting Three Groups"
Sorting Three Groups is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Made by an Amazon engineer who watched the leaked-problem repo become an industry secret. He decided you should have it too.
Get StealthCoderThe problem tests whether you can partition an array without comparison-based sorting. The naive trap is reaching for Arrays.sort() or Collections.sort(), which is O(n log n) and signals you missed the constraint. The actual insight: if the three groups have known values or a natural order, you can use either a single-pass counting strategy or a two-pointer technique that builds the result by region. It connects Array fundamentals with Binary Search intuition (dividing the space into regions) and Dynamic Programming thinking (state tracking across one pass). Candidates often overthink the logic flow. The trick is recognizing that you don't need to sort; you need to *classify and rearrange* in O(n) time. That pattern separation is where most stumble on the live assessment.
Pattern tags
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Sorting Three Groups recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Made by an Amazon engineer who watched the leaked-problem repo become an industry secret. He decided you should have it too. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Sorting Three Groups interview FAQ
What makes this medium, not easy?+
The 41% acceptance rate reflects a subtle constraint trap. Candidates default to sort() and pass basic cases, but the problem enforces linear time complexity, forcing a rethink. The real challenge is spotting that you're doing classification, not sorting.
Is this actually asked at UiPath?+
Yes, it's in their reported assessment rotation. Given the company's focus on automation and workflow optimization, problems requiring efficient partitioning and state management align with their technical screening.
How does this relate to Binary Search?+
Binary Search isn't the main algorithm here, but the topic hints at dividing the array into regions and finding boundaries. Some solutions use partition logic similar to binary search's divide-and-conquer mindset to separate the three groups.
What's the one-pass trick?+
Instead of iterating multiple times, use pointers or counters to track where each group starts and ends. As you scan the array once, place each element into its correct group region in O(n) time and O(1) or O(n) space.
Should I memorize a solution?+
No. Understand the partition pattern: identify what defines each group, use pointers or counters to mark boundaries, and swap or rearrange in one pass. That mental model transfers to similar problems faster than rote code.
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